Millions of pounds are being made every year by criminals doctoring condemned meat and selling it on for public consumption, according to a report by the Observer newspaper.

Joint investigations between environmental health officers and police officers from a least five forces in the UK have highlighted the worrying extent of meat "laundering" and aim to bring the gangs behind the illegal trade to justice.

Authorities explain that criminals buy meat destined for pet food products or destruction cheaply. By simply cutting off the rotting or diseased sections, and if necessary dying the meat white again by soaking it in salt water and non-toxic bleach, the gangs can increase its value from about 30p (US$0.44) to £2 per pound.

They then obtain false documentation to deceive traders into thinking the meat is legitimate, and make deliveries in the evenings or weekends to avoid checks by health inspectors. They are believed to target small independent traders such as halal butchers, which are often run by owners with little formal training.

Yunes Teinaz, a senior environmental health officer in London, told the Observer: "There is a lot of money to be made." In the last four months alone Teinaz's team has made 30 confiscations and obtained 21 court orders ordering the destruction of unfit meat.

The investigative teams in Lancashire, Hampshire, Wales, Norfolk and Derbyshire believe that laundering has increased in the wake of the foot and mouth crisis, which saw thousands of animals slaughtered. They also warned that government plans to privatise meat inspection will only play into the hands of the criminals.

The Regent's Park mosque in London is spearheading a new leafleting campaign to teach both traders and consumers to recognise unfit meat.